This invention concerns rotary die cutting apparatus of the kind comprising a cylinder driven in rotation and carrying on its surface a removable forme having knives projecting radially therefrom. In operation, flat board is transported tangentially past the cylinder so that the knives perform a predetermined cut on the board.
Conventionally, the forme which is usually made from timber and preformed, is attached to the surface of the cylinder by screws which must be aligned with threaded apertures in the cylinder. When it is required to change or replace the forme a lengthy procedure is required to remove and replace a considerable number of screws.
In an alternative arrangement the forme may be mechanically clamped onto the cylinder wall using cumbersome clamping arrangements so that the cylinder requires careful balancing. provide, in rotary die cutting apparatus, a means for removably mounting a forme such that it may be easily and rapidly removed from the cylinder for replacement.
According to the present invention there is provided a rotary die cutting apparatus comprising a driven rotary cylinder, a removable forme circumferentially mounted on the cylinder, and having knives projecting radially outwards therefrom, a plurality of radially inwards facing steel bars attached to the forme and extending longitudinally of the forme parallel to the axis of rotation of the cylinder, radially outwards opening longitudinal grooves in the cylinder to receive said steel bars, and permanent electric holding magnets located in said grooves to retain the forme magnetically on the cylinder, said grooves being spaced around the cylinder on opposed ends of three separate diametral planes, two of said planes being angularly disposed with respect to a plane normal to the third diametral plane, one on each side of said normal plane and displaced therefrom by an angle of not more than 25.degree..